Chemistry and kinematics of the late-forming dwarf irregular galaxies Leo A, Aquarius, and Sagittarius DIG

Journal Article · Sun Jan 01 04:00:00 EST 2017 · Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/834/1/9· OSTI ID:22869597

Kirby, Evan N.; Cohen, Judith G. ^[1]; Rizzi, Luca ^[2]; Held, Enrico V. ^[3]; Cole, Andrew A.; Manning, Ellen M. ^[4]; Skillman, Evan D. ^[5]; Weisz, Daniel R. ^[6]

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1. California Institute of Technology, 1200 E. California Blvd., MC 249-17, Pasadena, CA 91125 (United States)
2. W. M. Keck Observatory, 65-1120 Mamalahoa Hwy., Kamuela, HI 96743 (United States)
3. INAF, Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, I-35122, Padova (Italy)
4. School of Physical Sciences, University of Tasmania, Private Bag 37, Hobart, Tasmania, 7001 Australia (Australia)
5. Minnesota Institute for Astrophysics, University of Minnesota, Minneapolis, MN 55455 (United States)
6. Department of Astronomy, 501 Campbell Hall, University of California, Berkeley, CA 94720 (United States)

We present Keck/DEIMOS spectroscopy of individual stars in the relatively isolated Local Group dwarf galaxies Leo A, Aquarius, and the Sagittarius dwarf irregular galaxy. The three galaxies—but especially Leo A and Aquarius—share in common delayed star formation histories (SFHs) relative to many other isolated dwarf galaxies. The stars in all three galaxies are supported by dispersion. We found no evidence of stellar velocity structure, even for Aquarius, which has rotating H i gas. The velocity dispersions indicate that all three galaxies are dark-matter-dominated, with dark-to-baryonic mass ratios ranging from 4.4{sub −0.8}{sup +1.0} (SagDIG) to 9.6{sub −1.8}{sup +2.5} (Aquarius). Leo A and SagDIG have lower stellar metallicities than Aquarius, and they also have higher gas fractions, both of which would be expected if Aquarius were further along in its chemical evolution. The metallicity distribution of Leo A is inconsistent with a closed or leaky box model of chemical evolution, suggesting that the galaxy was pre-enriched or acquired external gas during star formation. The metallicities of stars increased steadily for all three galaxies, but possibly at different rates. The [α/Fe] ratios at a given [Fe/H] are lower than that of the Sculptor dwarf spheroidal galaxy, which indicates more extended SFHs than Sculptor, consistent with photometrically derived SFHs. Overall, the bulk kinematic and chemical properties for the late-forming dwarf galaxies do not diverge significantly from those of less delayed dwarf galaxies, including dwarf spheroidal galaxies.

• OSTI ID: 22869597
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 834; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
BARYONS
BOX MODELS
DISPERSIONS
DISTRIBUTION
GALAXIES
MASS
METALLICITY
NONLUMINOUS MATTER
SPECTROSCOPY
STARS
VELOCITY